Photometer system



Jan. 13, W. E GARITY ET AL PHOTOMETER SYSTEM Filed July 3l, 1940 2 Sheets-Sheet l BY 4\ L www ATTORN Y.

Jan. 13, 1942. w. E. GARITY ETAL v 2,259,813 A Y PHOTOMETER SYSTEM Filed July 31, 1940 2 Sheets-Sheet 2 6 FIG. 3

WML/AM E. GHR/ry /vmfy WOLFf IN VENTOR5 ATTORNE Patented Jan. 13, 1942 N 2,269,813l i rno'roME'rEn SYSTEM William E. Gar-ity, Los Angeles, and Halley Wolfe,

North Hollywood, Calif., assignors to Walt Disney Productions, Burbank, Calif., a corporation of California Application July s1, 1940, serial No. 348,614

(ci. zia-23) 12 Claims.

This invention pertains to improvements in devices for determining the luminosity or brightness of a surface or field of view, and is particularly directed to devices and methods whereby the brightness or luminosity of a surface or field may be obtained directly, irrespective of the distance between the instrument and field whose luminosity is being determined, within reasonable limits.

Prior methods of determining luminosity have not been satisfactory because the methods either involved complicated and unwieldy comparison devices or were not selective and therefore could not be used in determining the luminosity of a desired portion or limited area, or simply gave comparative readings which could not be expressed in terms of candles per square foot or other definite unit of illumination.

The present method obviates the dimculties and disadvantages of the prior art and permits readings to be obtained directly in candles per square foot. Moreover, the method of the present invention permits a selected limited area of an object or field to be tested. The ability to obtain such reading on a selected or desired portion of a total surface .is of great advantage in photography since a large field of view, may be embraced by the camera lens, such iield of View having areas differing very materially in luminosity.

An overall or average reading for -the entire eld oi View would be of little avail to the photographer who is primarily interested in obtaining an accurate detailed photographic image of a particular portion of such field. The photographer, therefore, is primarily interested in determining the luminosity of the desired portion only of the iield, the remaining portions being considered relatively unimportant as regards perfect development of the final photograph.

The present invention, moreover, is directed toward a stable, portable instrument capable of being employed in various positions and at various distances from the field or object whose luminosity or brightness is to be measured. The device` need not be positioned at any iixed or predetermined distance from the object in order to obtain accurate readings.`

Generally stated, the device of the present invention depends upon the use of a photoelectric c ell operably associated with an amplier and a measuring circuit. Means are provided for limiting the eld or angle of view of thephotoelectric device, these means permitting only a predetermined and xed angle of view whereby light from predetermined areas only may exert effect fupon the device. Means are also provided whereby the device may be accurately calibrated and the unit of measurement on the scale of the measuring device changed at will, generally in accordance with the luminosity of the surface or iield being tested, so that full eectiveness of the scale of the measuring instrument may be utilized. Means are also provided for preventing overload of the device and in maintaining the electrical circuits in effective `operating condition.

An object of the present invention, therefore is to disclose and provide means and methods whereby the brightness or luminosity of any desired portion of a'n object or iield maybe readily determined.

A further object is to provide means for measuring the intensity of light on a surface irrespective of changes in the distance o the measuring device from the surface being measured, so long as-the surface is large enough to lll the angular field o view of the instrument and has uniform brightness.

A further object is to provide means of reading directly in units of light intensity or luminosity of objects within a particular space angle irrespective of placement of the testing means with regard to the object.

An object of the invention is to provide a light measuring device whose 'readings are substantially not injured or affected by temperature of surroundings, magnetic elds, or constant or repeated use.

A further object is to provide particular arrangements of elements whereby the various desirable objects of the present invention may be readily attained.

These and other objects, advantages, uses, modications and adaptations of the invention will become apparent to those skilled in the art from the following detailed description of an exemplary form of the invention and methods of use. in order to facilitate understanding, reference will be had to the appended drawings, in which: j

Fig. l is an enlarged vertical section of one form of portable unit for use in the methods of this invention.

Fig. 2 is a diagrammatic representation of the device and one manner of use.

Fig. 3 isan exemplary circuit diagram of the system,

Although the methods and devices of this invention may be used in determining the luminosity or brightness of various surfaces, objects and nelds under numerous conditions, particula:I reference will be had hereafter to the use of the device in photography, specifically the photography of drawings. paintings and the like in the production of animated motion picture cartoon photoplays.

Generally stated in the production of animated cartoon illms various pictorial representations are made on transparencies commonly referred to as cells. Each cell carries a pictorial representation of one or more elements. These cells are placed in superimposed relation and photographed. The cells may be spaced one from the other and separately illuminated, generally, but not necessarily, from the camera side. In view of the fact that a large number of cells may be employed and thatthese cells may be carried upon or covered by additional sheets of transparent material, considerable loss of light reflected from a cell most distant from the camera takes place by absorption and reflection, in passing through other cells and transparent supports between it and the camera lens. For this reason it is important that each of the cells or planes be properly illuminated. If, for example, it is desired that the background drawing (generally farthest removed from the camera) clearly appear in the finished photograph, then the light intensity or luminosity of such background drawing should be appreciably greater than the luminosity of the cells or drawing nearer the camera lens. The method and devices of the present invention are particularly well suited for use in determining and establishing the illumination on each cell and in making certain that the luminosity of a cell is uniform over its entire surface.

For example, as shown in Fig. 2 diierent cellsl may be positioned in spaced relation within the field of view of a camera C. The cells are indicated at I. 2. 3 and 4. As shown in the drawings, a portable testing unit is generally indicated at 5 and is shown positioned upon the cell 2. The testing unit is connected as by means of the cable 8 with the measuring device generally indicated at 1. By moving the device 5 over the cell 2, the luminosity of selected areas of the cell may be readily determined and directly observed upon the instrument 1. If it is found that one side of the cell is insufficientlyA illuminated, the light sources 8 or 9 may be suitably adjusted.

` The. portable unit 5 may then be moved either up on cell I or down upon cell 3 to make additional determinations. Since each cell or plane is provided with independent iight sources, the illumination of the various planes may be accurately controlled before photography begins.

The measuring system includes the portable Vdevice 5 and the measuring unit 1. Generally stated, the portable device 5 includes a photoelectric cell whereas the measuring device 1 may include suitable amplifiers, measuring circuit, indicating devices, switches, etc. An illustrative circuit is shown in Fig. 3 whereas Fig. 1 is an enlarged sectional view of the portabledevice 5. As shown in Fig. 1, the device 5 may comprise a photoelectric cell Iii positioned within a housing generally indicated at II, said photoelectric cell being mounted upon astandard I2 supported by a base I3. In the particular form illustrated, the standard I2 is hollow so as to receive the cable 6 and a handle I4 is provided for the purpose oi facilitating movement of the entire unit. The housing II may be of any suitm able type but in order to stabilize the unit and inhibit variations in response in the photoelectric cell I 0 due to temperature changes. it has been found desirable to provide a substantially light-absorbing, heat-insulating housing auch as, for example, a housing composed of an inner member I5 and an 'outer spaced wall member I3, the inner opposing surfaces of the walls I5 and I6 being highly polished or plated. lThe 1nside surface of the wall member I5 and the exterior surface of the wall member I 8` may 'be made light-absorbing and non-actinic.

Means are provided for limiting the area of view exposed to the photoelectric cell III whereby light from a fixed space angle only is admitted to the photoelectric cell. In the form illustrated, the device includes a nose piece I1 carried by the lower side of the housing I I immediately beneath the photoelectric cell I0, such nose piece including limiting bames Il and Il having ports 20 and 2| respectively. A collecting lens 22 may be positioned in the upper end of the nose piece I1 orin the bottom of the housing Il for the purpose of positively directing light entering the nose piece onto the cell I0 through the aperture 23 made in the bottom of the housing II.

The interior of the nose piece I1 may be made non-reflective as, for example, by the use of a black velvet lining indicated at 24 or by the application of suitable black ilat paint.

It will be noted that the nose piece I1 and bailies I8 and I9 denitely limit the area of view exposed to the photoelectrlc cell III. The limiting lines of view are indicated at :c and y and it has been found that in most instances the space angle or the angle between :c and y may well vary from about 10 to 25 degrees. In most instances, angles of between about 15 and 20 degrees are entirely satisfactory. When the device is resting upon its base I3 and upon an object whose surface is to be measured, then, as indicated in Fig. 1. only the luminosity of the limited area A embraced by the space angle of the limiting means I1 is recorded by the photoelectric cell I0.

The internation of the portable unit s 'with the rest of the system will be evident from a study of Fig. 3. Current from any suitable source is supplied to the measuring instrument contained within a suitablev housing 1 as by means of line 3U leading to a power switch 3| and a voltage regulator 32. The voltage regulator is operably connected to a suitable transformer and rectifier,

generally embraced by the lines 33 adapted to supply current to the rest of the system through the lines 34 and 35 as well as to the filament of the amplifier tube 36. Conductors to the filament of the tube are not shown in detail but are indicated at m and n.

A plurality of resistances in series is connected between the positive and negative potential connections 34 and 35, these resistances constituting a bleeder circuit generally indicated by the numeral 31. Individual resistances are indicated at R1, Rz, Ra, etc. 'Ihe photoelectric cell is indicated at I0 and it is to be noted that the cathode of the cell is connected to taps on the bleeder circuit through the variable resistances R2 and Ra cated at 36 and a grid of this tube is connected to the'anode of the cell as by line 38. The plate of tube 36 is operably connected by lead 39 to a The vacuum tube of the amplifier is indiassente through switch Si and a sensitivity control cir-1v the tubme 35i (in this case nentode tube) may be connected as by lead l0 to one o the variable resistances, such as rlillecathode oi the tube leads to a selector switch Se which is capable or" connecting the cathode with any one oi a plurality oseparately operable circuits connected to various parts oi the bleed'er circuit Si'. Each of these separately oper.. able cathode or ieedbmlr circuits may include a variable resistance. Foihexainple, the switch Sa may connect contact fil directly with the bleeder circuit between resistances Rv and Ra. Contact 02 may lead to a variable resistance it and a fixed resistance Ris electrically associated with the operable portion of the variable resistance R1 and such means include the line d@ including suitable resistances R16 and R11 connecting the line 30 with the bleeder circuit.

block, the micromaeter id lsmade to read iull scale or 100 microarops by adjusting the variable resistance Rit which shunts the meter. the scale oflthe micro-aromates can now be {calibrata-7 ed between and 50 candles ner sanare toot.

The selector switch Si is then moved to tap ft2 corresponding to the 100 candle per square oot scale and again with the nose piece i the photo-cell darkened, the bias' voltage is adjusted by means of Re until the micromammeter reads l zero with substantially no adjustment of Rn.

ammeter.

The selector switch S3 and the switch S2 are mechanically coupled together so that the circuit to micro-ammeter M is broken whenever the cathode circuit is broken by the switch Ss. Switch Sz operating in. this manner gives some additional protection but it is not necessary for satisfactory operation.

The various circuits connected to the taps di to t5 of the selector switch Sspermlt a. selection in operative ranges'oi the device and accurate control within such ranges by the variable feed backresistors embodied in the cathode circuits. In thel device shown in Fig. 1 and diagrammatically represented in Fig. 3, the vacuum tube 36 is positioned in the portable device. It is to be understood that the vacuum tube 30 need not be carried in the portable device, but instead may be a part of the bulkier portion of the equipment.

In calibration of the device, by'one method which has been successfully employed, the nose of the portable device including the photoelectric cell, is directed upon a standard reiiecting surface such as that of a magnesium carbonate block illuminated with a standard lamp, the surface of the block being perpendicular to the axis of the lamp. `The axis of the nose piece il is placed in as perpendicular a position to the plane of the block as it is possiole so to do without casting shadows upon the block. in the field of view of the photometer. A xed bias voltage of approximately -2 having been previously determined is a desirable value to use on the tube 3B, the resistances Re and Rv are adjusted so that their sum gives thisv value of bias when no light is permitted to enter into the nose piece il. For these adjustments the selector switch S3 is maintained in contact with tap di. Under such. conditions, the micro-ammeter M is caused to read exactly zero by manipulating the variable resistance R11, then by positioning the carbonate block and standard light source so as to impart a brightness of candles per square foot on said By increasing the brightness on the magnesium carbonate block to candles cer square foot, the reading of the micro-animator is noted and the feed baci; resistance in the circuit connected to tap d2 is adjusted to cause a reading ci exactly 100 candles per square ioot on the micro- After each change ci feed hach re sistance the bias voltage is adjusted es by Re to sive the same nouliaht plate current. Resistance R1 is nowadjusted to maire Re plus its the same as its adjustment for the 50 ioot candle scale. Similar operations are carried out with the various other cathode circuits so as to provide a plurality of scales on the micro-ammeter rang ing from 50 to 5000 candles per square toot, say

5o, 10o, 25o, 5cc, loco and sooo.` when au the scales have been adjusted in the manner dey scribed, the mlcro-ammeter will read full scale for each scale setting at the full scale brightness and very little adjustment need be made with the zero or rio-light position of the meter in switching from one scale to the other. Great accuracy oi readings is obtainable by reason of the numerous' scales provided.

In an actual embodiment of the invention uslng a pentode amplifier tube No. 954 and a No.

922 photoelectric cell, the following values ci re y Y The feed back resistances in' the circuit connected to tap 02 included a fixed resistance R15 of 720 ohms and a variable resistance it set at 250 ohms. The corresponding values for the next circuit connected to tap v@t were 2900 and 630 ohms. The following circuit (tap d5) included a fixed resistance of 6000 ohms and a variable resistance set at 1330. The remaining feed back circuits increased at resistances of progressively increasingvalue of a. similar order. Under the specic conditions herein lreferred to, the shunt resistance R14 was set at about 1100 ohms whereas the fixed resistance En was of 9000 ohms. R12 had a value of 20,000 ohms.

The device described herein is of particular value in measuring the uniformity or flatness of lighting for a large area, since the portable device may be moved from one area to another to make certain the illumination thereon is uniform. The nose l1 restricts the light angle to which the photoelectric cell responds and thereby permits accurate measurements to be taken of limited areas throughout a. given field. 'When drawings, titles er the like are to be photographed, the ileld to be occupied by the drawing, title or the like may be readily measured. In the event the photography is to involve the production of two or more color separation negatives, it has been found desirable to embody light nlters in the nose i1 of the device, t-hese light nltersbeing similar to those employed in the camera to be used in taking the color separation negatives. The eiect of such light filters upon the luminosity o! the field can thus be readily determined. 1

It is 'to be understood that the lens 22 may be dispensed with undersome conditions, and that numerous other changes can be made in the construction and arrangement of the device. The method of calibration speciiically described here has been found effective, but other systems of calibration may also be used.

All changes and modifications coming within the scope of the appended claims are embraced thereby. i

We claim:

1. A system for measuring light intensity comprising: a photoelectric cell having an anode and a cathode, and a measuring circuit operably connected to said photoelectric cell and including a vacuum amplifier tube including a plate and a cathode, a high voltage connection to said plate, a low voltage connection to,said cathode, a current-measuring device operably connected in the plate circuit of said tube, a plurality of separately variable resistances in series connected between the high and low voltage connec.. tions for the tube, said resistances constituting a bleeder circuit, a. plurality of separate variable resistances in the cathode circuit and between said tube and variable points on the bleeder circuit. a selector switch adapted to selectively connect a cathode of said tube with a selected cathode resistance, a switch in the circuit of said current-measuring device, said switch being mechanically coupled with said selectorswitch to break the circuit to the measuring device upon breaking of the cathode circuit and to prevent overload of said current-measuring device, a iixed connection including a resistance between the bleeder circuit and the grid of said tube and the anode of the photoelectric cell to maintain a iixed voltage or potential on the grid and anode when no light enters said photoelectric cell and a connection betweenthe cathode of the photoelectric cell and a variable resistance in the bleeder circuit adapted to maintain a desired polarizing voltage on said photoelectric cell.

2. A system for measuring a light intensity comprising: a portable unit including a photoelectric cell having an anode and a cathode, a ventilated light-absorbing and heat-insulating housing for the photoelectric cell, means for limiting the area of view exposed to said photoelecof said tube with a selected cathode resistance, a switch in the circuit of said current-measuring device said switch being mechanically coupled with said selector switch to break the circuit to the measuring device upon breaking of the cathode circuit and to prevent overload of said current-measuring device, a nxed connection incl ing a resistance between the bleeder circuit and the grid or said tube and the anode of the photoelectric cell to maintain a fixed voltage or poten.. tial on the grid and anode, and a connection between the cathode of the photoelectric cell and a variable resistance in the bleeder circuit adapted to maintain a desired polarizing voltage oi' between about 15 and 30 volts on said photoelectric cell.

3. A system for measuring light intensity comprising: a source of current; a plurality of resistances in series connected across the source of current, said resistances comprising a bleeder circuit; a photoelectric cell; a measuring circuit operably connected to the photoelectric cell and to the current supply, said measuring circuit including an amplifier tube having a plate and a cathode; a switch in the measuring circuit; a plurality of separate cathode circuits connected to various parts of said bleeder circuit; and a selector switch connected to the cathode of said tube and adapted to connect the same with any one of said cathode circuits.

4. A system for measuring light intensity comprising: a source oi.' current; a plurality of resistances in series connected across the source of current, said resistances comprising a bleeder circuit; a photoelectric cell; a measuring circuit operably connected to the photoelectric cell and to the current supply, said measuring circuit including an amplier tube having a plate and a cathode; a switch in the measuring circuit; a plurality of separate cathode circuits connected to various parts of said bleeder circuit; and a selector switch connected to the cathode of said tube and adapted to connect the same with any y one of said cathode circuits, said selector switch tric cell, said means being carried by the housing, and a measuring circuit operably connected to said photoelectric cell and including a vacuum amplifier tube including a plate and a cathode,

a high voltage connection tok said plate, a low voltage connection to said cathode, a currentmeasuring device operably connected in the plate circuit of said tube, a plurality of separately variable resistances in series connected between the high and low voltage connections for the i and measuring 'circuit switch being mechanically coupled together to open simultaneously.

5. A system for measuring light intensity comprising: a source of current; a plurality of resistances in series connected across the source of current, said resistances comprising a bleeder circuit, a part at least of said resistances being separately variable; a photoelectric cell, a measuring circuit operably connected to the photoelectric cell and to the current supply, said measuring circuit including an ampliiier tube having a plate and a cathode; a switch in the measuring circuit; a plurality of separate cathode circuits connected to various parts of said bleeder circuits; and a selector switch connected to the cathode of said tube and adapted to connect the same with any one of said cathode circuits.

6. A system for measuring light intensity comprising: a source o! current; a plurality of resistances in series connected across the source of current, said resistances comprising a bleeder circuit. a part at least of said resistances being separately variable; a photoelectric cell; a measuring circuit operably connected to the photoelectric cell and to the current supply, said measuring circuit including an amplifler tube having a plate and a cathode; a switch in the measuring circuit; a plurality of separate cathode circuits connected to various parts of said bleeder circuit; and a selector switch connected to the cathode of said tube and adapted to connect the same with any one of said cathode circuits, said selector switch and measuring circuit switch being mechanically coupled together to open simultaneously. I

'7. A system for measuring light intensity comprising: a source of current; a plurality of resistances in series connected across the source of current, said resistances comprising a bleeder circuit, a part at least of said resistances being separately variable; a photoelectric cell; a meas-` uring circuit operably connected to the photoelectric cell and to the current supply, said measuring circuit including an ampliiier tube having a plate and a cathode; a switch in the measuring circuit; a plurality of separate cathode circuits connected to Various parts of said bleeder circuit, each of said cathode circuits including a separately variable resistance; and a selector switch connected to the cathode of said tube and adapted to connect the same with any one of said cathode circuits.

8. A system for measuring light intensity comprising: a source of current; a plurality of resistances in series connected across the sourceof current, said resistances comprising a bleeder circuit, a part at least of said resistances being separately variable; a photoelectric cell; a measuring circuit operably connected-to the photoelectric cell and to the current supply, said measuring circuit including an amplifier tube having a plate and a cathode and a bridge circuit including a micro-ammeter; a switch in the measuring circuit; a plurality of separate cathode circuits connected to various parts of said bleeder circuit; and a selector switch connected to the cathode 0f said tube and adapted to connect the same with any one of said cathode circuits.

9. A system for measuring light'intensity comprising: a source of current; a plurality of resistances in series connected across the source of current, said resistances comprising a bleeder circuit, a part at least of said resistances being separately variable; a photoelectric cell; a measuring circuit operably connected to the photoelectric cell and to the current supply, said measuring circuit including an amplier tube having a. plate and a cathode and a bridge circuit in-y cluding a micro-ammeter; a switch in the measuring circuit; a plurality, of separate cathode circuits connected to various parts of said bleeder circuit; and a selector switch connected to the cathode of said tube and adapted to connect the same with any one of said cathode circuits, said selector switch and measuring circuit switch being mechanically coupled together to open simultaneously.

10. A system for measuring light intensity comprising: a source' of current; a plurality of resistances in series connected across the source of current, said resistances comprising a bleeder circuit, a part at least oi -said resistances being separately variable; a photoelectric cell; a meas'- uring circuit operably connected to the photoelectric cell and'to the current supply, said measuring circuit including an amplier tube having a plate and a cathode and a bridge circuit inl cluding a micro-ammeter; a switch in the measuring circuit; a plurality of. separate cathode circuits connected to various parts of said bleeder circuit, each of said cathode circuits including a separately variable resistance; and a selector switch connected to the cathode of said tube and adapted to connect the same with any one of` said cathode circuits, said selector switch and measuring circuit switch being mechanically coupled together to open simultaneously.

1l. A device for measuring light intensity or brightness of a eld comprising: a portable member `provided with a base and a head, a downwardly directed nose piece carried by said head, a photoelectric cell in said head in operative relation to said nose piece, said nose piece being adapted to restrict the entry of light to a predetermined space angle; a source of current; a plurality of resistances in series connected across the source ofcurrent, said resistances comprising a bleeder circuit; a measuring circuit operably connected to the photoelectric cell and to the current supply, said measuring circuit including an ampliner tube having a plate and a cathode; a switch in the measuring circuit; al plurality of separate cathodelcircuits connected to various parts of said bleeder circuit; and a.v

determined space angle; a source of current; a'

plurality of resistances in series connected across the source of current, said resistances comprising a bleeder circuit; a measuring circuit operably connected to the photoelectric-cell and to the current supply, said measuring circuit including an amplifier tube having a plate and a cathode; a switch in the measuring circuit; a plurality of separate cathode circuits connected to various parts of said bleeder circuit; and a' selector switch connected to the cathode of said tube and adapted to connect the same with any one of said cathode circuits, said selector switch and measuring circuit switch being mechanically coupled together to open simultaneously.

, WILLIAM E. GARITY.

HALLEY WOLFE. 

